1. Field of the Invention
The present invention relates to an exhaust purifying device for purifying exhaust gases emanating from an internal combustion engine, and a method of producing the same and, more particularly, to an exhaust purifying device of the type having a core provided with a honeycomb structure and applied with a catalyst, and a method of producing the same.
2. Description of the Related Art
It is a common practice with an internal combustion engine, e.g., an automotive internal combustion engine to attach an exhaust purifying device or so-called catalytic converter to an exhaust pipe or a muffler forming part of the exhaust system of the engine. The catalytic converter promotes the oxidation of exhaust gases emanating from the engine to reduce carbon monoxide, hydrocarbons and other toxic components contained therein. Typical of conventional catalytic converters is one having a metallic casing and a metallic core received in the casing and provided with a honeycomb structure. The casing is attached to the exhaust system of the engine as, for example, part of an exhaust pipe or part of a muffler.
Specifically, the core of a catalytic converter mounted on an automobile has a flat metallic sheet and a corrugated metallic sheet overlying the flat sheet. The two sheets are held by a metal core and then sequentially rolled up together to form a spiral honeycomb structure. However, the problem with such a structure is that the two sheets are likely to shift relative to each other when initially being wrapped around the metal core. The relative shift of the sheets directly translates into deformation of the honeycomb structure, i.e., it is likely that the honeycomb core suffers from critical structural defects including collapsed corrugations and gaps. Such defects potentially constitute a cause of irregular strain in the honeycomb core. When the core having such defects is applied to a motorcycle or similar automotive vehicle, it comes apart, gets out of shape or otherwise deforms due to aging. This not only aggravates the structural defects but also often lowers the purifying ability of the catalytic converter.
In light of the above, Japanese Utility Model Laid-Open Publication No. 163437/1989 discloses a catalytic converter having a honeycomb core produced by abutting the end of a corrugated sheet and that of a flat sheet, connecting the abutting ends by spot welding or similar technology. Although this scheme eliminates or at least reduces the problems particular to the above-described conventional core, it is not practical without resorting to two different kinds of sheets, i.e., the corrugated sheet and flat sheet and, moreover, an extra spot welding step. In addition, delicate and troublesome work is needed for the two sheets to be abutted and affixed together in accurate alignment. Should the two sheets be brought out of alignment, the resulting honeycomb core would have an auger-like or similar incomplete configuration.